1. Field of the Invention
This invention relates to the field of solid state electronics, particularly to solid state detector arrays.
2. Description of the Prior Art
Focal planes used for detecting radiation require arrays of detectors which are constructed of special semiconductors that are sensitive to the wavelength being detected. Previous focal planes have used discrete detectors in linear arrays. The cost of these arrays, however, on a per detector channel basis has been high, reflecting the low yields associated with detector fabrication, number of associated parts, and the critical hand wiring involved. Additionally, as the requirement for the number of detectors increase, this approach is ultimately limited in performance by the relatively large size of discrete detectors, interconnect complexity, and power dissipation.
One approach taken to overcome the limitations of discrete detectors is to integrate the detector and signal processing functions on-chip. This approach, based upon the charge transfer concept, makes possible high density self-scanned infrared arrays with integral low noise readout. The use of charge transfer devices allows signals from a large number of detectors to be multiplexed on-chip and read out through a single output amplifier, thereby reducing the parts count and interconnect complexity and making possible arrays with thousands of individual detectors.
One class of integrated arrays, monolithic extrinsic arrays, utilizes an extrinsic substrate (silicon or germanium) to provide sensitivity to radiation. The resultant signal charge is injected into a lightly doped epitaxial layer for charge transfer multiplexing and readout. Although monolithic extrinsic arrays offer the advantages of integrated construction, they have relatively low quantum efficiency, high operating temperature, and high crosstalk.
A second class of integrated arrays, hydrid arrays, employs separate sensing and charge transfer media. The detector array, fabricated in an efficient photosensitive material, is electrically and mechanically coupled to a silicon charge coupled device (CCD) multiplexer (see, for example, U.S. Pat. No. 4,067,104 to John Tracy). Such hybrid design permits optimum selection of materials for both the detecting and signal processing functions. However, it requires a large number of fragile interconnects and an efficient input circuit to inject the detector signal into the silicon CCD multiplexer.